Heat transfer unit



- April 24, 1956 D. C. PORTER HEAT TRANSFER UNIT Filed April 6, 1954 H v m INVENTOR.

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United States Patent HEAT. TRANSFER UNIT Donald C. Porter, Arcadia, Califi, assignor to D'ubl'D'ee Engineering Corporation, Arcadia, Cali., a: corporation of California Application April'6, 1954, Serial No; 421,353 12 Claims; (Cl; 219 -49);

This invention relates to heating platens such as are used. with. presses for moldingr or: pressing: variousi materials.

The usual type of. press platen is heated'with steam, which passes through pipesin: theheating block or'mold. Thepresent invention. relates to-a platen which may have a flat top or be shaped to form certain. types of. articles to'be. molded'or pressedand which is heated electrically. Platens have been knownto be electricallyheated, but the result has been a wawy form' of. heat distribution. The present platenis. one inwhich: a particularly uniform distribution of heat is obtained over all unit areas of the surface thereof and at the desired temperature.

This. is primarily accomplished by the use of a novel heat transfer medium: between the heating units them,- selves and themetal of. the platen, which is'usually steel, and the arrangement of the components: of the-medium. This mediumis such that it. has a heat transmission or transfer which.- will. conduct the heat away from the electrical unit at a rate to prevent. burning of: the unit and permit an even distribution of the heat by conduction and fiowagezintmalll sections of "the platen; It: also has increased heatinsulation at'certain: sections. The novel heat transfer medium is a combination of Woods metal and'red brass'particles, although bronze particles may also be used. The" temperature to which the platen is heated is'between 350* degrees C. and 400 degrees C., which is far below-theintegration' temperature of Woods metal which is approximatelyl000 degrees C. However, Woods metal melts at 165' degrees F.,, permitting the metal to expand and how, and thus, enhance the heat distribution.

The principal object of the invention, therefore, is to facilitate the heating of a mold or press platen.

Another object of the invention is to provide an improved system for heating platens electrically.

A further object of the invention is to provide a novel, electrically heated platen by the use of a novel heat transfer or distributing material.

The novel features which are believed to be characteristic of this invention, both as to the manner of its organization and the mode of its operation, will be better understood from the following description, when read in conjunction with the accompanying drawing, in which:

Fig. 1 is a plan view of a platen partially in crosssection and embodying the invention.

Fig. 2 is a detail view of a section of the platen of Fig. 1 for permitting expansion of the heat distributing material.

Fig. 3 is a detail view showing the electrical connections to an electrical heating unit, and

Fig. 4 is a cross-sectional view taken along the line 4-4 of Fig. 3.

Referring now to the drawings, in which the same numerals identify like elements, a platen 5 is a metal plate preferably of steel, of rectangular form, and coordinately drilled with intersecting holes 3 and 4 completely through the main body of the platen, end portions 9 and 12 being drilled as shown at 14 to permit attachment of the platen to a press. The. ends of the holes 3: and14 are: threaded; the ends of: holes 3,. shown at. the top: of the drawing; having threaded plugs: 6 therein; while the endsiof: the holes 3= atthe bottom of the drawing: have threaded plugs 7 therein: ThehorizontathoIesJare lugged at-one end by plugs shownv at 8, while a substantially verticaally posie tioned pipe 10 is connected! to'interioflydhreaded plug 11. Inth'e holes 4 running transversely of. the drawing. are Calrod units 13; which, asshownin Fig. 3, are conneeted in parallel by conductors 15 in a conduit 16'.

In' ahole- 17, which:v may! extend: completely across the platen, is a thermostatic bulb- 18,. which, through the pipe: 19, builds? up pressure to' actuate contacts within a switch 21 for. regulating the' temperature of. the-platen: It is noted. that. the Calrod: units. 13: do not occupy the entire spacesor. cavities oil the transverse: holes 4-, these spaces: or cavities being filled. with a combination. of Woods metal and. red. brass; particles having; a. diameter of not less than twenty-five percent of the distance bettween the outer surfaces of the Calrod units.- anct the inner surfaces of holes. 4.. hy'usingbrassparti'cles of .this size, the voids run: approximately fifty percent of the cavities, so that the combination: includes fifty percent wood s' metal. and: fifty percent brass; Thiscombination of Woods metal and brass also. fills' theholes: 3;.as shown in the drawing, so that allr cavities-are interconnected? Since the Woods metal expands with heat; the vertically arranged pipe 10'permits: the Wood?s metal to run up the pipe during the. heating operation: and to how back when. the platen cools.

The cross-sectional view shown in Fig. 4 shows: the Calrodv casing 20'with3the electricakconductorsrfl embedded in ceramic material Between the external surface of: the casing 20. and: the internal. sunfacerofthe opening 4, is showni the-Woods metal. 25: anththe bronze particles 26 in the proportion mentionedmbove';

' The reason the. combinationz of: m'aterials'mentioned above has: proved: so. satisfactory as a: heat transfer or. distributing element: is that .steel*,.. at: 1 00:- d'egrees. C., has a heat conductivity value off-.101 calories. Woodszmetal; however; has a. heat conductivity value of .03E19 c'alorie, which is the heat" transmitted-per sec'o'n'di through aplat'e one centimeter thick. across an" area ofi one: square centi meter when the temperature: difference is: one degree centigradez This value,- however, is: too. low compared with steel, and would provide to'o" greataan: insulator,- and thus, result in burned Calrod units. If the Calrod units were directly in contact with the steel platen, a wavy heat pattern would exist on the surface of the platen. However, red brass has a heat conductivity of .246 calorie at zero degrees Centigrade and above. Thus, since the Woods metal and brass are in fifty-fifty proportions, the average of the two materials is .1389 calorie, which exceeds that of steel. Thus, since the Woods metal melts at degrees F., it will flow among the bronze particles and along the openings and transfer the heat by physical movement as well as by conduction. By eliminating air, it prevents oxidation of the Calrod units, the steel, and the brass, and because of its liquid state, enhances heat distribution.

A feature of the invention is shown at 28 and 29 in Fig. 4, this feature being that the Woods metal with its low heat conductivity of .0319 calorie is formed into segments of pure Woods metal at the upper and lower portions of each cavity or hole. These segments are formed by placing screens of approximately twenty mesh, but always smaller than the size of the brass particles, along the upper and lower chords of the holes. This results in providing unusual uniformity of heating of the platen, since the combination of Woods metal and brass at the sides of the holes transmits heat comparatively fast to the thick solid portions of platen between the holes. The pure Wood's metal segments, however, between the heating units and the comparatively narrow portions at the top and bottom portions of the platen retard the heating thereof until the main body portions of the platen are heated from the sides. Thus, there is a fast flow .of heat up through the platen portions between holes and a comparatively slower flow directly to the surface of the platen. To further enhance uniform ity, the Calrod units at the edges of theplaten where radiation is-greater are of a larger capacity than those passing through the center of the platen, the variation in size of the units depending upon the size of the platen. A cover plate 34 isprovided to protect the electrical connections from damage.

It was found that, in the use of the new material namely, fifty percent Woods metal and approximately fifty percent red brass. particles-the platen could be raised to the desired. temperature of approximately 320 degrees C., in thirty minutes, while it required approximately four hours-to reach the same temperature with steam. It was also found that the platen was more uniformly heated and the platen maintained at a more constant temperature. I claim:

1. An electrically 'heatable platen comprising a metal member, electrical heating units in cavities through said member, and a combination of Woods metal and brass particles in intersecting cavities between the outer surfaces of said electrical heating units and the inner surfaces of said cavities in said member.

2. An electrically'heatable platen in accordance with claim 1, in which the size of said brass particles is such that approximately fifty percent of said combination is Woods metal and fifty percent is brass and said member is of steel.

-3. An electrically heatable platen in accordance with claim 2, in which said brass particles have diameters not exceeding twenty-five percent of the distance between the outer surface of said electrical heating units and the surface of said'cavities.

4. A system for heating a metal platen having intersecting holes drilled coordinatelytherethrough, compris ing a metal member having intersecting holes therein, closure means for said holes to form cavities, an electrical heating unit in all the cavities running in the same direction, and a heat conducting material of Woods metal and brass particles interposed. between said electrical heating units and said steel in said cavities containing said electrical heating units and in the cavities running transversely therethrough.

5. A system in accordance with claim 4, in which means for. permitting expansion of said Woods metal is provided at the end of one of said cavities.

6. A system in accordance with claim 4, in which the size of said brass particles with respect to the size of said cavities is such that approximately fifty percent of said material is Woods metal and approximately fifty percent is brass.

7. A system in accordance with claim 6, in which the diameter of said brass particles does not exceed twentyfive percent of the distance between the outer surfaces of said heating units and the inner surfaces of said cavities in which said units are positioned.

8. A heating platen or mold comprising a metal block having intersecting holes therethrough, means for closing the ends of said holes to form intersecting cavities in said block, electrical heating units in the cavities positioned in one direction in said block, space being provided between said units and said block, and material in said spaces and the other cavities in said block, said material being normally solid but becoming liquid at the temperature to which said block is heated.

9. A heating platen or mold in accordance with claim 8, in which said material is a mixture of Woods metal and brass particles.

10. A heating platen or mold in accordance with claim 9, in which means are provided for eliminating said brass particles from portions of said spaces between said units and inner surfaces thereof closest to the surfaces of said block.

11. A heating platen or mold in accordance with claim 10, in which said mixture is approximately fifty percent Woods metal and fifty percent brass particles.

12, A heating platen or mold in accordance with claim 11, in which said brass particles have diameters not exceeding twenty percent of the distances between the outer surfaces of said units and the inner surfaces of said holes in which said units are disposed.

References Cited in the file of this patent UNITED STATES PATENTS Jolas Feb. 14, 1933 

